In the future, various wireless local area network (WLAN) services are expected to occur. However, the available frequency spectrum resources for supporting WLAN services have decreased. Therefore, in order not to damage signals (that is, to suppress interference) between WLAN services, the frequency spectrum resources and service coverage are expected to be strictly limited.
In order to efficiently provide WLAN services, electromagnetic waves having uniform amplitude should be radiated within a service coverage range, and a side lobe level should be suppressed. An antenna for WLAN services is required to provide a flat-topped beam pattern with a limited field of view (LFOV) characteristic.
A passive multi-terminal-network array structure, a coupled double-mode waveguide array structure, a passive reactive load element array structure, a pseudo optical network array structure, a protruding-dielectric-rod array structure, and a multi-layered disk array structure (MDAS) have been recently proposed as conventional flat-topped beam pattern forming devices.
In comparison with other flat-topped beam pattern structures, the MDAS can generate a desired current distribution by using mutual coupling between radiating elements in a free space, so that highly-efficient, small-sized, light-weighted, inexpensive antenna system can be implemented by using the MDAS.
In an antenna forming a single flat-topped beam pattern, an active MDAS and several passive MDASs surrounding the active MDAS are overlapped through mutual coupling so as to constitute an overlapped sub-array. However, such an antenna isn't efficient to form the flat-topped beam pattern.
Therefore, there is a need for a new shaped-beam antenna structure suitable for an antenna forming a single flat-topped beam pattern.